This invention relates to an illumination panel of a sidelight type, and a display device using the same.
Hitherto, as an illumination panel which emits light from its front face, there has been a panel called a sidelight type.
Hitherto, the illumination panel of this sidelight type has been composed of: a photoconductor whose at least one end face is an incident face of for light from a light source and whose front face is an emitting face of the light taken in from the end face; and a light source section arranged oppositely to the end face of the photoconductor.
As this photoconductor, there is generally used a transparent plate in a flat plate form comprising acrylic resin or the like. As the light source section, there is used a fluorescent lamp in a straight tube form, an LED array wherein plural LEDs (Light Emitting Diodes) are arranged, or the like.
In this illumination panel, light from the light source section is introduced into the photoconductor, and the light is emitted from the substantially whole area of its front face. The light from the light source section is taken in the photoconductor from its single end face, and is repeatedly reflected in this photoconductor. Thereafter, the light is emitted from the front face.
The illumination panel is used for a backlight in a display device using a transmission type display means wherein the transmission of light is controlled for display, such as a liquid crystal display element, or the like. For example, a liquid crystal device using a liquid crystal element has a structure in which the illumination panel is arranged at the back of the liquid crystal display element and oppositely to the element.
Display devices having this illumination panel are classified into devices in which only display using light from the illumination panel is carried out and devices in which both display using light from the illumination panel and display using outer light such as natural light or room light are carried out, that is, what is called two way display type devices. Conventional two way display devices have a structure in which a semi-transmission reflective plate is arranged between the display means and the illumination panel arranged behind the means.
In this two way display device, when sufficient outer light is obtained, reflection type display using the outer light is carried out, and when sufficient outer light is not obtained, the light source section of the illumination panel is switched on to carry out transmission type display using the light from this illumination panel. In the case of the reflection type display using outer light, the outer light incident from the front side of the display means is reflected on the semi-transmission reflective plate and then the light is transmitted through the display means again to be emitted outwards, whereby display is carried out. In the case of the transmission display using light from the illumination panel, the light transmitted through the semi-transmission reflective plate, among light source light from the illumination panel, becomes light incident on the display means, and then the light is transmitted through the display means to be emitted outwards, whereby display is carried out.
The aforementioned conventional display devices have a problem that bright display cannot be obtained whether outer light is used or light from the illumination panel is used.
This is because the conventional illumination panel does not have a function of reflecting outer light to be emitted ahead of the display means and thus the semi-transmission reflective plate is essential to make any display device into a two way display type.
In other words, the semi-transmission reflective plate causes the incident light to be reflected or transmitted dependently on its reflectivity/transmissivity characteristics, and therefore in the case of the reflection type display using outer light, the light of a quantity corresponding to the transmissivity of the semi-transmission reflective plate, among the incident outer light, becomes loss light that is transmitted through the semi-transmission reflective plate and is not reflected. On the other hand, in the case of the transmission type display using light from the illumination panel, the light of a quantity corresponding to the reflectivity of the semi-transmission reflective plate, among the light source light emitted from the illumination panel, becomes loss light that is reflected on the semi-transmission reflective plate and is not transmitted.
For this reason, in the conventional two way display devices, the efficiency of using light is low in both the case where outer light is used and the case where light from the illumination panel is used. And the convention display gets dark in either case of the display using outer light or the display using light from the illumination panel.